Verification of the Monte Carlo Model in the BrainLAB IPlan System for Clinical Applications

Purpose: To verify the Monte Carlo (MC) model in the BrainLab iPlan treatment planning system (TPS) in homogeneous and inhomogeneous media for clinical applications and to evaluate the BL Imaging Couch Top (BICT) in the TPS.

Methods: One 30x30x12 cm³ solid water phantom and one 30x30x18 cm³ inhomogeneous phantom made of solid water and cork board were CT scanned and the images were transferred to the iPlan TPS. Single field plans (from 2x2 to 15x15 cm²) were calculated on the two phantoms for AP, PA and oblique gantry angles. An IMRT and a dynamic arc plans were also calculated. Each plan was calculated using both the Pencil Beam Convolution (PBC) and the MC models and with insertion of the BICT. All plans were delivered at the Novalis TX and the isocenter doses were measured using the A-14 ion chamber.

Results: For the homogeneous phantom, planned doses from the PBC and the MC models agree within 2% and all the planned doses agree with the measured doses within 2%. For the inhomogeneous phantom, the planned doses from the PBC and the MC models differ from 1.6% to 4.8% depending on the field sizes. The measurements agree with the MC plans within 1.2%. The differences between the measurements and the PBC plans vary from -1.3% to -4.0%. With the BICT included in the plans, the measured doses for the single PA fields differ with the MC planned doses from 0.5% to 3.7%. However, for the six-beam IMRT and the six-dynamic arc plans, the measured total doses agree with the planned doses with in 2%.

Conclusions: This work verified that the MC model in the BrainLab iPlan TPS is ready for clinical applications in both homogeneous and inhomogeneous media. The couch model in the TPS was evaluated and is acceptable.